Electrical discharge device



ELECTRICAL DISCHARGE DEV ICE Original Filed July 14, 1937 5 Sheets-Sheet1 Fig.46 d 002 moo c o 4 00 0 00 by 1 a .\a/.

F1240 Fig 5 o o o o o o i O O\b/O O\b/Q 0 v Inventor:

Wil'liam C.Hahn,

6P by W His bborney June 27, 1944. HAHN Re. 22,506

ELECTRICAL DISCHARGE DEVICE Original Filed July 14, 1937 5 Sheets-Sheet2 Fig.6

HglOa a 0 00 0 0 o o 0 0 o o Ffg. IO b Inventor-z William C. Hahn,

by W 6. JML

His Attorney.

June 27, 1944, w. c. HAHN Re. 22,505

ELECTRICAL DISCHARGE DEVICE Original Filed July 14, 1937 5 Sheets-Sheet3 W Hg. \3 a LIMIT OF FAST OBJECTS -plmrorszow oaJEcrs Inventor .WilliamClHahn,

y His Attorney June 27, 1944. w c, H Re. 22,506

ELECTRICAL DISCHARGE DEVICE I Original Filed July 14, 1937 5Sheets-Sheet 4 1 Fig. \4

Fr' ls Inventor": Williarn C. Hahn,

June 27, 1944. 'w. c. HAHN Re. 22,506

ELECTRICAL DISCHARGE DEVICE Original Filed July 14, 1937 S Sheets-Sheet5 'IIIIIIIII, v

ELECTRON STREAM Inventor": William QHahfi,

y His Attorney irregularities 'Reiccued June- 27, 1944 ELECTRICALDISCHARGE DEVICE William 0. Hahn, some, N. Y., assignor to GeneralElectric Company, a corporation oi' New York ' I I I Original No.2,220,839, dated November 5, 1940,

Serial No. 153,602, July 14, 1937.

Application for reissue August 27, 1942, Serial No. 456,880

21.0laims.

This invention relates to electrical discharge devices and to improvedmethods and means for controlling discharge currents. While not limitedthereto, the invention is particularly useful in its application toamplifiers, detectors, oscillators and converters for use at very shortwave lengths, on the order of meters to 5 centimeters.

Inasmuch as an adequate explanation of the invention necessarilyinvolves the repeated use of various terms of a more or less technicalcharacter, I have in the following paragraphs set forth the meaningswhich I desire to attach to certain such terms.

By "conduction curren I intend to designate a stream of moving charges,such, for example, as an electron beam current passing through anevacuated or gas-filled conduction space.

By conduction current modulation I mean to designate the controlledproduction of irregularities in a conduction current stream. Thus, aconduction current modulated electron beam is a beam in which at anygiven time systematic in electron velocity or electron density existfrom point to point along the beam.

By "charge density modulation I mean the controlled production ofirregularities in the distribution of charges within a conductioncurrent stream. Thus, a charge density modulated electron beam is a beamin which at any given time the electron density varies from point topoint along the beam in accordance with some controlled pattern ofvariation.

By velocity modulation I mean the controlled production ofirregularities in charge velocities within a conduction current stream.Thus, a velocity modulated electron beam is a beam in which at any giventime the electrons at various points along the axis of the beam aremoving with different velocities according to some controlled pattem ofvariation.

quantitatively, any type 'of modulation may be measured as the ratio ofthe magnitudeoi the maximum departure of the modulated quantity from itsaverage value to the magnitude of such average. Thus, a charge densitymodulated electron beam in which the electron density along the beamaxis varies from zero to twice the averagedensity may be said to possessone hundred per cent charge density modulation.

current variations so produced by the grid have the effect of inducing asimilarly varying current in the grid circuit. Under ordinary conditionsand at low frequencies this induced current, which is caused byinstantaneous diilerences in the electron charges approaching andreceding from the grid, is relatively small and is approximately degreesout of phase with the grid voltage, so that it produces no appreciablepower loss. However, as the operating wave length is decreased so thatthe electron transit time becomes appreciable with respect to thereciprocal frequency (1/!) of the control grid potential variations, theinduced current not only increases but becomes more nearl in phase withthe grid voltage. These two effects combine to produce the result thatthe apparent shunt resistance of the grid circuit varies inversely asthe second power of the frequency of the operating voltage. It is forthis reason that at very high frequencies (i. e. very short wavelengths) the conventional type of grid attains such a low shuntimpedance and involves such a large power loss as to be practicallyunusable.

It is a primary object of the present invention to provide an improvedmethod and means for controlling an electronic discharge current wherebythe production of current variations in .the control circuit by thepassage of the discharge current through the control elementmay beprevented and the shunt impedance of the control circuit maintained at ahigh value even when control potentials oi very short wave length areinvolved. 7

. Ancillary to this primary object it is a more particular object of theinvention to provide a control electrode structure so constructed andoperated as to produce primarily velocity modu-' lation of the dischargecurrent without the occurrence of appreciable charge density variationsin the vicinity of the control electrode.

An important consideration from the standpoint of the utility of theinvention lies in the fact that a relatively small amount of velocitymodulation may under proper circumstances be converted into asubstantially greater amount of charge density modulation, evenapproaching one hundred 'per cent modulation as a limit. Accordingly, itis feasible to amplify weak input or control potentials by using them toproduce velocity modulation of an electron beam and by thereafterconverting the velocity modulation into charge density modulation of ahigher order I of magnitude.

It is a further object hereof to provide methcontrol electrodestructure, whereby velocity modnlation-.:produced by a control electrodemay be ell'ectively convertedjintm charge density mod- Y ulation.

A still further object consists in theeilective application of the basicprinciples of the inven-- tion to amplifiers, detectors, oscillatorsandconverters suitable for operation at,;very short wave lengths.

The features of novelty which I desire toprotect herein will be pointedout with particularity in the appended claims. The invention itself,together with further objects and advantages thereof, may best beunderstood by reference to the following description taken in connectionwith the drawings in which Figs. 1 to 3 are schematic representationsillustrating certain basic elements of the invention; Fig. 4 is adischarge device embodying one application of the invention; Figs. 4a,4b and 4c are diagrammatic representations useful in explaining theoperation oi the device ofFlg. 4; Fig. 5 is a graphical representationillustrating certain of the characteristics of the device of Fig. 4;Fig. 6 is a perspective view in partial section of a structuralmodification of the device of Fig. 4; Figs. 7, 8 and 9 showschematically further modifications of the' device of Fig. 4, especiallywith respect to the provision of various means for converting velocitymodulation into charge density modulation; Fig. 10 illustrates stillanother means for converting velocity modulation into charge densitymodulation; Figs. 10a and 10b are diagrams which are useful inexplaining the operation of the device of Fig. 10; Fig. 11 is amodification of the device of Fig. 10; Figs. 12 and 13 illustrate stillother means for converting velocity modulation into charge densitymodulation; Fig. 13a is a diagram which is useful in explaining theoperation of the device of Fig. 13; Figs. v14, 15 and 16 show variousdischarge devices illustrating the use of the invention in convertingkinetic energy in a charge density modulated electron beam intoelectrical I energy to be utilized in an external circuit; Fig.

17 shows one mode of applying the invention to a detector; Fig. 17a.shows the current-voltage characteristic of such a detector; Fig. 18shows one mode of applying the invention to an oscillator: Fig. 19 showsone mode ofapplying the invention to a converter; Figs. 20 and 21,respectively are side elevation and plan views of an alternativeelectrode arrangement and Fig. 22 is an incomplete view showing apractical mode of use of certain of the electrodes of the device of Fig.20.

In the drawings above referred to I have indicated certain for theoperation of the various electrodes. It should be understood, however,that the values given are exemplary only, and that they may be variedwithin wide limits, even to the extent of changing their order ofmagnitude.

One important feature of the invention with respect to the production ofvelocity modulation 01' an electron stream consists in the provision ofa modulating space which is substantially shielded from the streamsource. or cathode. By virtue of such shielding, current or potentialvariations which occur in the modulating space have no tendency toefl'ect changes in the cathode emission or to produce charge densityvariations in the space as a result of such changes.

A modulating space as specified in the forevoltage ranges as beingsuitable going'may comprise, for example, a space which is arrangedtotraversed by an electron beam. and the entrance are maintained atfixed potentials with respect to one another. Thus, in the particulararrange-. ment shown in Fig. 1, a modulating space is provided-betweentwo apertured conducting barriers .or diaphragms fli nd.- .tiwhichdlaphragms are electrically connected to one-another and mainopening |5in the diaphragm l0 and leave through mediate region.

In order to produce maximum velocity modulation 01 an electron beamtraversing a modulating space such as that. bounded by the dlaphragmsill and II, the potential level of an intermediate region of the spacemay be cyclically raised and lowered with respect to the boundarypotentials at such a rate that the velocity of any given eleclarstructure of trode is caused to vary above and below that of thediaphragms with the proper periodicity, as by connection to a source ofcyclicallyvarying control voltage 2|, efl'ective velocity modulation ofthe transmitted beam may be obtained. The proper periodicity" asspecified in the last sentlence is determined by the followingconsideraons.

Consider an electron which has iust passed through the diaphragm II at amoment when the potential of the electrode II is at a D0sitive maximumwith respect to that of the diaphragm. Such an electron will obviouslybe accelerated in the approach space between the diaphragm and the openend of the electrode tube. In the case illustrated, the interior ofspace, so that the velocany fixed frequency of control potential theelectron transit time itself may be varied to fulfill the conditionemphasized in the foregoing paragraph. This may be done as a practicalmatter either by changing the length of the tube I! or by varying thespeed of the electron beam.

Assuming that the various elements have been properly adjusted as I haveproposed, it will be seen that there is available an extremely eiliclentmechanism for producing velocity modulation of an electron beam. With agiven peak value of the control potential, certain electrons in the beamwill be accelerated by an amount corresponding to a potential variationapproaching and exit'boundaries of which above ground. {The l3 which mayenter through an 7 the tube llconstitutes twice that value, while otherswill be retarded by an equal amount. The ratio actually existing betweenthe maximum electron acceleration or retardation (expressed in volts)and the peak value of the control potential may be called the "velocityratio" oi. the control electrode. It will vary somewhat with theelectrode geometry, but for the construction illustrated will be onlyslightly less than two.

It may also be noted that the production of velocity modulation by themethod and means so far described is accomplished without appre-j ciablepower loss in the control circuit. This is due to the fact that thecurrent variations produced in the vicinity of the control electrodestructure are actually extremely small so that the resulting currentinduced in the control electrode is substantially negligible. As hasbeen previously suggested herein, the utility of the invention liespartly in the fact-that slight velocity variations, produced withoutsubstantial power loss, may be subsequently and, in a sense,automatically converted into much greater magnitudes of charge densityvariation.

The precise form of control electrode structure shown in Fig. 1 is in noway essential for the purposes of the invention, and I have shown inFig. 2 another structure which may be alternatively used. In this figurethe diaphragms 22 and- 23 correspond generally to those alreadydescribed in Fig. l. The control electrode structure, however, comprisesa pair-of wire grids 25 and 26 which are spaced to enclose a region ofsubstantially the same axial extent as the region enclosed by the tubeIQ of Fig. 1. Since these members are electrically connected together,this enclosed region constitutes a substantially fieldiree space;consequently, if the potential of the grids is cyclically raised andlowered with the proper periodicity as previously specified, velocitymodulation of a passing electron beam will occur.

A still further possible modification of the control electrode structureis shown in Fig. 3, in which the control electrode differs from thosepreviously described in comprising a conducting member of negligibleaxial extent. This member is illustrated as a ring 30, but mayalternatively comprise an apertured diaphragm or other equivalentstructure.

With this arrangement the optimum conditions to be fulfilled aresomewhat difierent from those previously postulated. Specifically, it isdesired that the electron transit time between either of the boundarydiaphragms 3| and 32 and the plane of the control electrode correspondto a half cycle of the control potential. This being true, an electronwhich enters the modulating space at the instant the control electrodehas assumed a positive potential will be accelerated throughout theduration of its passage from the plane of the diaphragm 3| to the planeof the Also, since a voltage reversal control electrode. occurs as theelectron passes the control electrode, it will be again acceleratedduring the entire period of its passage from the plane of the controlelectrode to the plane of the diaphragm 32. In the same way an electronwhich enters the modulating space one-half cycle later will be retardedboth as it approaches and as it recedes from the ring 30. A similarresult will be obtained if the transit time between each 01' theboundary diaphragms and the control electrode is an oddmultiple ofone-half cycle rather than a single half cycle as described in theforegoing.

Having now explained some of the basic principles of the invention, Ishall in the iollowing illustrate its utility in connection with variousdischarge devices. For simplicity, I shall describe the use 0! theinvention mainly with reference to discharge devices adapted to be usedas amplifiers. It should be understood, however, that the variousfeatures referred to are not limited to such application and may incertain cases be even more advantageously employed in connection withdetectors, oscillators, converters, etc.

Referring particularly to Fig. 4 I have shown a discharge device whichcomprises a sealed metal envelope including an elongated tubular portion40 and a base portion ll sealed thereto. Within the envelope there isprovided means for developing an electron beam of substantially constantaverage intensity and velocity. Such means may include any known type ofelectron gun," and that illustrated constitutes only one example of manypossible constructions. In the arrangement shown, the electron sourcecomprises a thermionic cathode incluling a filamentary heater 3 and anenclosing cylinder 44. Surrounding the cathode as a whole there isprovided a focusing electrode in the form of a conducting tubular member48. This latter element is supported directly by an insulating bushing41 and indirectly by means of a second tubular member 49 which isrigidly secured to a transverse barrier 5l.

In the use of the device the filamentary heater 43 is energized by meansof a suitable energy source, such as a battery 52 connecting with theheater through bayonet contacts 54 and 55 and lead-in connectionsassociated therewith. The focusing electrode 46 is in the normal casemaintained at cathode potential or at a potential which is slightlynegative with respect to the cathode, and when so charged is efiectiveto concentrate the electrons emitted from the cathode surface into abeam of generally cylindrical outline. Such a beam may be given thedesired velocity by impressing anappropriate potential between thecathode and the transverse diaphragm 51. The magnitude of the potentialto be applied will vary within wide limits depending on the conditionsof operation. For a particular case it may be on the order of from 200to 400 volts and may be provided by means of a battery 51 connectedbetween one of the cathode terminals and the metal structure of thedischarge envelope.

Somewhat spaced from the conducting member or diaphragm 5| there isprovided a second diaphragm 59 which is in the case illustratedmaintained at an identical potential with the first diaphragm by beingelectrically connected thereto. These diaphragms are respectivelyprovided with central apertures GI and 62 and in combination define achamber which is shielded from the beam source or cathode. In thecontemplated use of the device this shielded chamber may constitute amodulating space in which the velocity of the constituent electrons ofan electron beam traversing the space may be affected or modulated. in adesired manner. Such velocity modulation may be accomplished, forexample, in any of the ways described in connection being so.

cally varying control potential; This may be derived, for example, froma high frequency input circuit shown as including an antenna a tunedcircuit comprising a condenser an inductance 88. A battery II is alsoemployed to impress on the control electrode structure a direct currentpotential of the same order of magnitude as that impressed on thediaphragm ii and II.

Assuming the device to be in. normal operation, the electron beamissuing from the opening I will be velocity modulated; that is, it willbe characterized by successive variations in electron velocity frompoint to point along the beam. The degree of modulation may be extremelyslight if only weak control potentials are available, but it may bechanged into charge density modulation of a considerably higher order ofmagnitude by conversion means now to be described.

Such means may comprise, for example, a collecting electrode or anode llpositioned in alinement with the opening II. This anode, which issubstantially shielded from the modulating space by the diaphragm It,may be biased, as by a battery It to such a low voltage that onlyapproximately one-half of the electron beam is collected, the other halfbeing reflected back along the beam axis. If the beam is velocitymodulated as described above, the faster electrons may hit the collectorwhile the slower ones fail to reach it. Since the faster and slowerelectrons are respectively bunched in alternately spaced groups alongthe axis of the beam, it will be seen that both the collected currentand the reflected current will be charge density modulated.

This particular method and mean of converting velocity modulation intocharge density modulation by reversing the lower velocity components ofthe beam is the invention of George F. Metcalf and is claimed by him inhis applica- V tion Serial No. 201,953, filed April 14, 1938.

The method of separating fast and slow electrons described in theioregoing will, perhaps, be better understood by referring to thediagrammatic representations of Fig. 4a. 4b and 40. In Fig. 4a, forexample, there is shown an imaginary stream of electrons which isvelocity modulated so as to comprise alternate groups of fast and slowelectrons. The fast electrons are represented by the groups a, forexample, and the slow electrons by the groups 1:. The line d represent;the plane of the collecting anode hereinbefore described. In Figs. 4band do, I have shown the components of the electron beam which have beenrespectively collected and reflected by the anode d. It will be seenthat each of these components is characterized by successive variationsin charge density and is therefore charge density modulated within thedefinition of that term previously given herein.

From a consideration of the idealized situation represented in theforegoing it might seem that even the slightest degree of velocitymodulation of the electron beam would produce IOOper cent charge densitymodulation of both the collected and reflected components of current.That this is not so is due in part to the random electron velocityvariations inevitably present in the beam even before modulation takesplace. Because of such variations the ideal grouping of fast and slowelectrons shown in Fig. 4a cannot actually occur, some slow electronbeing necessarily mixed with the fast groups and vice versa. This somerandom fast electrons are colr the fast groups. As

- charge stream.

- complished.

- L. Thorson and is lected from even the slow electron groups and somerandom slow-electrons are reflected from velocity modulation anismdescribedan modulation which produces through the mechmay beconsiderably lower than loll-percent and which is variable with thedegree of velocity modulation involved.

The actual relation between velocity modulation and charge densitymodulation is determined by the slope of the cit-in static curve of thecollector as illustrated in Fig. 5. This slope, which for any given tubeis fixed by the random electron velocity variations occurring in thedismay be very steep for practical tube constructions. Consequently, ifsuch a bias is applied that the collector operates, say, at the point X,substantial amplification may be no- The degree of amplificationobtainable is as a matter of fact very much larger than has heretoforebeen possible with wave lengths on the order of from 5 meters to 5centimeters or less.

prevented by tilting the collecting anode slightly as illustrated sothat the reflection of the beam occurs in a direction calculated tocause it to impinge on a solid portion of the diaphragm ll. (Thisparticular feature is the invention of Harry fully described and claimedin his application Serial No. 264,877, filed March 30, 1939.)

The conduction current variations induced in the anode 15 by means ofthe charge density tery it permits the unimpeded passage frequencycurrents to these terminals. (By the term "circuit" as used herein andin the appended claims I intende to designate not only such circuits asare formed by the combination of lumped impedance elements,

structures such as standing wave transmission lines and the like.)

The structural features illustrated in Fig. 4 are not essential to theinvention, and in Fig. 6 there is shown a generally similar device whichis enclosed in a glass envelope I! rather than in a metal container aspreviously described. It will be seen that the device comprises acathode (not shown), a focusing member 81, and an anode ll, and amodulating grid It, all of which correspond to the elements similarlyidentified in conby means ot-apertured which resemble the diaphragms IIand S9 of Fig. is provided with a flange ll surrounding its centralaperture, which flange assists in properly directing the electron beamwith respect to the surface of the collecting electrode ll.

The control electrode structure so far described hsve been of suchnature as to provide a result. a given amount oiv amount of chargedensity -be maintained at the same potential.

an enclosed substantially field-free space which is traversed by theelectron stream. In connection with relatively longer wave lengths, itis difllcult to stay within practical dimensions and still i'ulfill thecondition that the electron transit time through the electrode structureshall correspond to a halt cycle of the control potential. This is dueto the fact that the duration of such a hall cycle may be so great thatfor high electron velocities the control electrode would have to be oigreat length. This difliculty might be overcome in one way by reducingthe electron velocity as by operating the control electrode at a lowaverage potential with respect to the boundaries oi the modulatingspace. Such a mode of operation is to a certain extent objectionable,however, in that it inherently increases the electron transit timethrough the approach spaces existing between the boundaries 'and theextremities of the control electrode structure.

For reasons which need not be stated here, such an' increase in transittime tends to reduce the modulation factor oi the control electrode..

In Fig. 7 I have shown an alternative arrangement of the controlelectrode structure which may be advantageously employed with controlpotentials of relatively long wave length without encountering thedifliculty noted-in the foregoing. In this case the control electrodecomprises a tubular member having electrically separate sections I00, IMand I02 arranged-coaxiall with the electron path and extending to withina short distance of transverse diaphragms I04 and I which define amodulating space. In this figure and in those which follow, it should beunderstood that the transverse diaphragms are connected to the dischargeenvelope which is indicated in dotted outline.

In the operation of the device as thus constructed, the controlelectrodesections I00 and I02 are electrically connected together so asto Their "average potential, as determined, for-example, by means of abattery I01, may be of the same order of magnitude as that of theboundary diaphragms I04 and I00 so that the electron transit timethroughthe approach spaces is relatively short. The electron transittime .through the control electrode, on the other hand, ma beappreciably increased without adding to its length by operating thecentral section IOI at an average potential substantially below that ofthe end sections. This may be accomplished, for exfrom the othersections as to direct current potentials, it is effectively connected tothem as far as alternating potentials are concerned by means of acondenser 'I I0. Consequently, the potential of the control electrode asa whole may be cyclically raised and lowered at radio frequency by meansof a tuned input circuit comprising, for example, an inductance H2 and acapacitance Ill, energy being supplied to this circuit from an antenna.Ill coupled thereto. is insulated from ground asv'far as direct currentsare concerned by means of a blocking condenser IIG. Also, the endsections of the control electrode are insulated from ground with respectto radio frequency potentials by means of a choke I I0.

A further advantage oi the construction de- The input circuit scribedconsists in the fact that it is elective to prevent deiocuslng orspreading or the electronbeam. Due to space charge effects within thebeam there is a strong tendency for such spreading to occur alter thebeam has moved an appreciable axial distance. With the control electrodearrangement indicated, the fields existing between the various electrodesections are such as to comprise an electron lens system adapted tomaintain the beam in focus during its passage through the electrodestructure.

The-mechanism of velocity modulation described in connection withFigures 4. 8 and '7 may be still further enhanced by employing a numberof successive modulating grids arranged in cascade. One such arrangementis illustrated in Fig. 8, in which the chambers between the diaphragmsI20 to I23 constitute a succession oi modulatin spaces. The tubularelectrodes I20, I28 and I21 comprise a corresponding series ofmodulating grids.

As shown, the three grids are operated at the same potential and are.energized from a common input source or the type already described. Inorder to accomplish the result that any given electron shall besimilarly aflected as to velocity as it passes through each of themodulating spaces a somewhat diflerent dimensional rela-' tionship mustbe maintained than has been previously referred to. Specifically, withtubular electrodes as illustrated. it is necessary that the transit timethrough each of the electrodes correspond to some even number of halfcycles of the control potential, and that the transit time between theextremity oi any electrode and its nearest-boundary diaphragm comprisean odd number of such hali' cycles. Assuming the simplest case, viz:that in which the transit time through each grid corresponds to two halfcycles and the transit time through each approach I will be acceleratedduring the entire period of its transit from the diaphragm I20 to theopening 01 electrode I25. During its passage through the electrode itwill be substantially unaiiected as to velocity and will reach thefurther extremity of the electrode Just as the electrode enters anegative potential phase. The transit time through the space betweentheelectrode I20 and, the diaphragm I2I will, it the speciflc'conditionsare fulfilled, consume a time corresponding to a hall cycle of thecontrol potential. Consequently, the entrance of the electron into thenext modulating space will be coincident with the initiation of apositive phase of the control potential. Under these circumstances it isclear that the selected electron will be repetitively accelerated duringits entire course through the electrode system. Similarly, an electronwhich enters the first modulating space one-halt cycle later will beuniformly decelerated during its entire transit through such system.

An effective cascade arrangement of grids may also be realized byutilizing a succession of structures of the type illustrated in Fig. 3wherein the axial extent of the control grid itseliis substantiallynegligible. Adding this possibility to those enumerated in the foregoingparagraph, it may be stated that the optimum conditions for a cascadegrid construction are (1) that the electron transit time through eachcontrol grid should be either negligible or approximately equal to aneven multiple of half cycles of the control potential, and (2) that thetransit time through the approach spaces between the boundary diaphragmsand the extremities of the control grids should correspond to an oddnumber of half cycles.

It has been noted that when the collecting anode serves simultaneouslyas a beam reversing means and as an output electrode for connection toan output circuit, its apparent shunt impedance is undesirably low. Thisdifllculty may be overcome in one way by the arrangement indicated inFig. 9, in which the reversing and output functions are accomplished byseparate elements. This may be done, for example, by positioning beforethe output anode a reversing electrode I28 which is biased at such avoltage as to reverse at least the lower velocity electrons and totransmit higher velocity electrons. The transmitted component of beamcurrent is charge density modulated in accordance with the principlespreviously explained and when collected by the anode I29 will producealternating potential variations across the terminals of the outputcircuit.

With the arrangement shown the anode I29 may be biased to a sufllcientlyhigh positive potential so that it collects all electrons transmitted bythe electrode I28. The reverse component of current is so deflected bysuitably tilting the electrode I28 as to intersect a solid portion ofthe boundary diaphragm I 20, thus being prevented from returning intothe modulating space where it might tend to produce regenerativeoscillations.

The conversion of velocity modulation into charge density modulation hasso far been described exclusively in connection with the use of meansfor separating the modulated beam into collected and reflectedcomponents. In Fig. 10 there is illustrated an alternative means foraccomplishing such conversion which is dependent upon a somewhatdifferent principle. The device shown comprises a modulating spaceconfined by diaphragms Ill and I82, and a modulating grid I33 oi thesame general character as those previously referred to. Following themodulating space, however, there is provided a drift space" bounded bythe diaphragm I82 and by a third diaphragm I34. Within the space thereis provided a cylindrical member or "drift tube" I35 similar to thecontrol electrode I33 but preferably of substantially greater length. Itis a function of this member to provide in the path of the electron beaman extended field-free space or a space which is substantially free fromany but static potentials.

If the potential of the control electrode I33 is raised and lowered withrespect to the diaphragms III and I32 in accordance with the procedurealready described, the electron stream which enters the drift tube IIIwill comprise alternately spaced groups of "fast" and "slow" electrons.It will be apparent that under these conditions there will be a definitetendency for the more rapidly moving electrons to catch up with thosewhich are moving more slowly. It is the purpose of the tube II! toprovide a "drift space" in which a definite bunching of electrons canoccur as a result of this tendency. The nature of the results desired tobe obtained will best be understood by referring to Figs. 10a and 10bwhich comprise an idealized representation of two successive conditionsof a velocity modulated electron beam. I

In Fig. 10:: the electron beam is shown as it is assumed to issue fromthe modulating space. It will be noted that at this tim it comprisesaiternate spaced groups of fast electrons a and slow electrons b aspreviously explained. In Fig. 10b the condition of the same beam at asomewhat later period is illustrated. As shown, the fast electrons havecaught up with the slow electrons so that definite irregularities incharge density distribution have been produced correspondin modulation.The change which has taken place is from its nature one that requiresonly the elapse of time and the absence of extraneous influences whichmight tend adversely to affect conditions within the beam. Theserequirements may be fulfilled in a practical manner by permitting thevelocity modulated beam to pass through a relatively long shielded spacesuch as is provided in Fig. 10 by the drift tube I35. The necessarylength of this tube is determined both by the degree of velocitymodulation and by the average velocity of the electron beam as a whole.Generally speaking, and considering only idealized conditions, the timerequired to realize complete charge density modulation as illustrated inFig. 10b would correspond approximately to the duration of a quartercycle of the control potential divided by the per unit velocitymodulatiom (Per unit velocity modulation is the peak velocity variationdivided by the average beam velocity.) The length of a drift tubeadapted to afford such time would be this time multipled by the averagevelocity of the beam through the tube. Since the per unit velocitymodulation produced by an input signal is a small fraction of unity, itis apparent that the drift tube length will ordinarily be relativelylong in comparison with the distance traversed by the beam during asingle cycle of the control potential. The beam velocity and,consequently, the drift tube length may be somewhat reduced by operatingthe tube at a lower potential than that of the boundary diaphragm iii inorder that the beam may be retarded as it enters the tube. Also, it isnot necessary as a practical matter that the drift tube be of suchlength as to permit complet conversion of the velocity modulation intocharge density modulation as represented in Fig. 10b. A considerablysmaller degree of conversion will be effective to produce substantialamplification of the input potential if that is the desired end resuit.

In an amplifier utilizing a drift tube as a con-' version means thecharge density modulated current issuing from the drift tube may butilized in an external circuit by collecting the entire beam at ananode I31. In this case the anode is preferably biased as :by means of abattery I38 to such a voltage that substantially none of the componentsof the beam will be reflected.

I have previously referred to the inherent tendency of an electron beamto become defocused or spread after passage through an appreciablespace. This difficulty insofar as it occurs in connection with the useof a drift tube may be substantially overcome by a drift tubeconstruction as illustrated in Fig. 11. In this figure the drift tubecomprises a plurality of electrically separate similar sections I40 toI44, alternately spaced sections being electrically connected togetheras shown. The end sections I40 and I44 are preferably operated at arelatively low potential with respect to the boundary diaphragms I45 andI46 so that the average beam velocityis to a high degree of chargedensity p reduced asthe beam enters the drift tube struc ture. Byoperating the intermediate sections ill and III at a somewhat higherpotential a-deflnite self-focusing effect may be obtained throughout.-

the length of the drift tube. This eii'ect-is due to lens actionproduced by the interacting'fielda of adjacent tube sectionsand iseifective to counteract the inherent tendency of the beam to spread-Consequently, an extremely long drift space can be provided withoutdanger of the beam current being collected by the walls of the drifttube structure.

The focusing system described in the preceding paragraph is theinvention of George F. Metcalf and is claimed by him in his applicationSerial No. 201,954, filed April 14, 1938.

A still further mechanism for the conversion of velocity modulation isillustrated in Fig. 12. In this figure a modulated beam issuing througha central aperture in the diaphragm I" is caused to pass through atransverse electrostatic field provided, for example, by electrodes lland I52.

-As is well known the amount of deflection produced by such a field isdetermined by the velocity of the charges being deflected. Consequently,an efi'ective separation of the higher and lower velocity components ofthe beam may be accomplished by this means. The lower velocity electronswill be most deflected and may be collected by means of an appropriatelypositioned anode I". A similar anode I" placed more nearly adiacent thenormal path of the beam will collect the less deflected and,consequently, higher ve-' ponents will comprise spaced electron groupsand will therefore be charge density modulated as previously explained.This charge density modulation may be most effectively utilized in anoutput circuit by connecting the anodes I54 and I to such a circuit inpush-pull relationship-as illustrated.

The deflection field referred to in the foregoing paragraph may beproduced by impressing a direct current potential between the elec'trodes Iii and IE2 by means of a battery III. Also. instead of anelectrostatic field one may alternatively employ a magnetic field asadefiecting means.

There exists still another mode of converting velocity modulation intocharge density modulation which may be conveniently explained inconnection with Fig. 13. The construction shown in this figure resemblesthat of Fig. 4 in that it includes a similar velocity modulating gridI56 and a tilted anode I51. It differs from it, however, in that theanode I51 is biased to such a low voltage (zero or several voltsnegative) as to repel all electrons in the approaching beam. I nowpropose to show that by such repellent action the velocity modulation ofthe beam may be converted into charge density modulation.

The demonstration may be clarified by reference to an analogy which isrepresented in Fig.

13a. In this figure the small light circles are assumed to indicaterelatively slowly moving rolling objects approaching an incline I58,whereas the black circles indicate more rapidly moving objectsapproaching the same incline. In the condition illustrated theprocession of objects" fast or the slow objects, the diiferently movingobjects will roll up the incline to different levels before reversing.By properly choosing the steepness of the incline a condition may bereached such that two successive objects which approach the incline withgiven differences in velocity may be caused to roll on the incline atprecisely-the same instant. It is clear that the resultant grouping, ifrepetitive ior succeeding objects, actually comprises ajtorm of densitymodulation.

' locity electrons. For reasons pointed out in connection with Fig. 10each of the separate com- While the analogy above drawn is imperfectinsome respects as referred to a velocity modulatedelectron beam, it issufficiently accurate sothat we may regard the action of such a beam inapproaching the retarding field as being equivalent to that 01diiferentl'y moving objects in approaching a retarding incline. Byproper adjustment of the potential of the retarding field with respectto the degree of velocity modulation and-to the axial spacing ofvelocity maxima and minima, an arrangement may be reached in whicheii'ective charge density modulation will obtain in the-reversed portion'of the beam; In

tio'nby reversing the entire electron beam can alsobe applied inconnection with oscillators, de-

tectors orothertypes of discharge device.

Ordinarily, the potential gradients produced by the use of .a negativelycharged reversing is velocity modulated" although it is not den-.

sity modulated."

Assuming that theincline is of such steepness and length as to beinsurmountable by either the electrode are so; steep that the. sortingefi'ects attributable to-it are not very great. In oper'ation,-however,the potential gradients may be favorably tapered, either by space chargedue to theeffect of the'reversing beam, or by special space chargeelectrodes appropriately positioned in thereversing space.

, In Fig. 14 there is shown an alternative means by-- which energy maybe abstracted from a.

charge density modulated electron beam. In this case the velocitymodulating means comprises a tubular grid ill of the same general typeas those previously described herein. The

.means for converting the velocity modulation into .charge densitymodulation comprises, for example, a multi-sectional drift tube Iiisimilar to that described in connection with Fig. 11. An anode-Ell!serves -to collect the entire electron beam-after. its'alternatingpotential energy has' been'efiectively-utilized as described in thefollowing.

The charge density modulated beam issuing from the drift tube III ispermitted to enter an energy conversion space defined between boundarydiaphragms I61 and I. .Within this conversion space=there.is provided atubular electrode structure I65 which, although similar to the controlgrid lit-in construction, is opposite to it infunction in that itspurpose is to convert the kinetic energy of the charge density modulatedbeam into electrical energy at alternating potentials -to be; utilizedin; an external circuit. The mechanism by which. such conversion isaccomplished is as follows:

Assuming that a group of charges passes through the central opening inthe diaphragm I" and approaches the electrode I55, it will tendconnection with Figs. 1 to 3 inclusive.

I discharge device of Fig.

to induce a current in such electrode. If the beam is of substantiallyconstant intensity or is "unmodulated, this tendency will be neutralizedby the equal and opposite effect of the charges leaving the electrodHowever, if the beam is charge density modulated so as to permit of asubstantial diil'erence between the approaching and leaving charges,rent may be induced in an external circuit connecting with theelectrode. Brief consideration will show that the most favorablecondition is that in which the electrode I65 has a length whichcorresponds at least approximately to the distance between successivecharge density maxima and minima in the beam or to some odd multiple ofsuch distance. If this is true, the approach of a charge maximum willcoincide with the recession of a charge minimum and the resultant effectas viewed in the external circuit will be at its greatest possiblevalue. The region enclosed by the electrode I85 should preferably extendto within a short distance of the diaphragms III and I so that theelectron approach spaces are as small as possible.

It should be noted that as a given charge group leaves the electrode I"and moves toward the boundary diaphragm I, it will induce in theelectrode a current pulse opposite in sign to that roduced during theapproach period. Accordingly, by use of an external circuit of propercharacteristics, including, for example, a condenser I" and aninductance I88, an alternating potential of appreciable magnitude may bedeveloped across output terminals I10.

It is an important feature that by the means described in the foregoinga single variation in charge density is caused to produce a doubleexcitation of the external circuit. Stated in another way, an electrodesuch as I 65 is eiiective to abstract energy at two different times fromthe same group of moving charges by a mechanism which is equivalent to a"current doubling" process. By employing a plurality of similar tubularanodes in cascade, it is possible to extend this principle still fartherand to collect or induce total currents of considerable magnitude. Theenergy thus developed in the output circuit is obtained, of course, by areductionin the average velocity of the electron beam. The actual energyconversion process may then be said to consist in changing the highvoltage low current energy of the beam into high current low voltageenergy in the output circuit.

The construction of the electrode I6! is not limited to the form shownbut may include any of the alternative arrangements described in In anycase most effective operation of the device with respect to energyconversion is attained when the electrode and the energy conversionspace are so proportioned with respect to the distance betweensuccessive charge density maxima and minima in the beam that any givenelectron is similarly aflected as it approaches and recedes from theregion affected by the electrode. The dimensional requirements for thisresult are in general the same as were prescribed in connection withFigs. 1 to 3.

Fig. represents a slight modification of the 14 with respect to theconstruction of the energy abstracting electrode. In this case, thereare provided a velocity modulating grid I18, a drift tube I16 and acollecting anode II'I corresponding in essential partica pulse ofconduction cur- I ulars to those previously described. The energyabstracting electrode, however, comprises a plurality of sections I", Iand III, respectively. Of these the end sections I'll and III areelectrically connected together and are maintained at the same directcurrent potential by means of a battery I82 while the center section Illis preferably maintained at a lower direct current po tential by meansof a battery I II. In this way one obtains the result of increasing thetransit time of electrons through the electrode structure and ofmaintaining the electron beam in focus during said transit. Theadvantages of such an arrangement, particularly in connection with lowerfrequency operating potential, have been fully explained in connectionwith Fig. 7 and need not be further elaborated upon here.

The various sections of the energy abstracting or converting electrodeare maintained at the same potential as far as alternating voltages areconcerned by means of a condenser I84 which is, of course, a directelectrical connection for radio frequency currents. Consequently,variations in potential produced in either of the end sections by anapproaching or receding charge group similarly aflects them and inconnection with a charge density modulated electron beam will produce analternating potential across the tuned circuit I86 and the outputterminals I81.

The mechanism of energy abstraction described in connection with Figs.14 and 15 may also be utilized with devices other than a drift tube, forconverting velocity modulation into charge density modulation. Forexample, in Fig. 16 there is illustrated the combination of a tubularenergy abstracting electrode I" with a beam reversing anode I9! of atype previously described herein. In the arrangement illustrated, anelectron beam proceeding from acathode I9! is velocity modulated bymeans of a grid I93 and is permitted to approach the anode I9I isoperated at a sumciently low potential to reverse at least the lowervelocity components of the beam. The charge density modulated reversedcomponent is permitted to enter an energy conversion space definedbetween boundary diaphragms Ill and I" but is of the diaphragm II.

The electrode I90 is preferably of a length equal to the distancebetween adjacent charge density maxima and minima in the beam or to anodd multiple of such distance. Consequently,

plained, duced in the electrode structure. By means of an externallyconnected tuned circuit III these current variations are transformedinto potential variations to be impressed across output terminals I99. I

which passes through the electrode on its way toward the collectinganode III. In order to prevent regenerative oscillations from beingproduced in this way we have provided means for relation'with only thevelocity modulated portion of the beam. This electrode is biased toapproximately the same voltage as the electrode I90 and is connected tothat electrode by means of a condenser 203. Consequently, any variationsin the potential level of the electrode I90 are accompanied by preciselysimilar variations in the potential level of the electrode 21 andsimilar modulation of the transmitted electron beam will be produced byboth electrodes. It will be noted, however, that if the approach spacesbetween the electrodes and the boundary diaphragms are substantiallynegligible, the modulating effects produced by the electrodes on a givenportion of the electron beam will be opposite in sign and will thereforecancel one another. Stated in another way, any acceleration of the beamwhich is produced by the electrode 2M will be neutralized by acorresponding retardation produced by the electrode I90.

So far the principles of the invention have been described exclusivelyin connection with discharge devices adapted to be used as amplifiers.It will be apparent to those skilled in the art that its use is by nomeans limited to such field of application, and in Figs. 1'? to 19 wehave illustrated some exemplary tube constructions applied to purposesother than amplification. In Fig. 17, for example, we have shown a tubecorresponding in essential particulars to that described in' connectionwith Fig. 4 in combination with circult elements adapted to cause thetube to operate as a detector. A velocity modulating grid 2") is shownas being connected to an input circuit which may be assumed to beenergized with a signal voltage which comprises a carrier frequencymodulated with audio frequency. It will be understood, therefore, thatin the operation of the tube an electron beam which leaves themodulating space by passing through a central opening in a boundarydiaphragm 2 II will be velocity modulated in accordance with thevariations in the carrier voltage impressed n the modulating grid. Inorder to accomplish rectification or detection of such a beam, the beamis caused to approach a tilted anode 2 l5 which is biased to such apotential as to reverse at least the lower velocity component of thebeam. As in cases previously explained, the anode is so tilted that thereversed component current is not returned into the modulated space. Theoperating characteristic of such an anode is'shown in Fig. 17a and it isunderstood that in the use of the device for the purposes indicated theanode is preferably biased to a portion of the characteristic indicatedat X. It is self-evident, that under these conditions the device willproduce rectification of the beam and will develop a potential of audiofrequency across output potentials 2H5. It has already been explained-inconnection with Fig. 4 that the same tube if operated on a linearportion of its characteristic may be used to produce effectivedistortionless amplification without detection.

InFig. 18 there is shown the discharge device of Fig. 17 slightlymodified to operate as an oscillator.- With the arrangement shown, thereis provided a velocity modulating space defined by boundary diaphragms220 and 22! and containing a velocity modulating grid 222. This grid isconnected externally to an oscillating circuit comprising, for example,a condenser 223 and an in uctance 224 and is adapted to be cyclicallyvaried in potential level in accordance with the oscillations of suchcircuit. The electron beam after being velocity modulated by passagethrough the modulating space is directed toward an anode 225, which isadapted to reverse a portion or all of the beam thereby convertingvelocity modulation into charge density modulation. The charge densitymodulated component is returned into the modulating space and caused topass through the grid 222. If this grid' is of such length that theelectron transit time therethrough corresponds to a half wave length ofthe tuned frequency of the oscillating circuit, energy at such frequencywill be returned to the circuit. The energy thus abstracted from thebeam will serve to maintain the system in self-sustained operation. Theenergy which is developed in the oscillating circuit may be utilized asa practical matter by being fed into an antenna 228 which is suitablycoupled to the circuit. A system such as that described mayadvantageously be used in the transmission of ultra high frequencies.

Somewhat greater complexity is involved in adapting the invention toconverter or superheterodyne operation although this may be done in apractical manner by an arrangement such as illustrated in Fig. 19. Inthis case the electron beam may be velocity modulated by a controlpotential having a carrier frequency component through the agency of acontrol grid 23!. The beam is then passed through a tubular electrode232 which may be connected to a local oscillator circuit 233 adapted tooscillate at a selected frequency higher or lower than the carrierfrequency.

For the purposes now contemplated the electrode 232 should beconstructed and arranged in accordance with the principles described inconnection with Figs. 1 to 3 hereof, so that additional velocitymodulation will be imparted to the beam during its passage through themodulating space which encloses the electrode. Referring to a tubularelectrode construction such as that illustrated, the electron transittime through the electrode should correspond to an odd number of halfcycles of the oscillator frequency. If this condition is fullfilled, thebeam will be given a component of modulation corresponding to theselected frequency of the oscillating circuit.

This doubly modulated beam is then caused to approach a tilted electrodeor anode 235 which is adapted to reverse at least the lower velocityportion of the beam. This anode is preferably biased by means of abattery 236 so as to operate on that portion of its characteristicindicated at X in Fig. l'la. As a result of such operation,

there will be a mixing or cross modulation of the .two modulationfrequencies of the approaching beam so that the reversed component ofthe beam will include both sum and difference frequencies. Consequently,if the circuit including the condenser 230 and inductance 239 is tunedto the difference or intermediate frequency, potential variations ofthis frequency may be developed across the terminals 240.

It is also true, as will be readily understood by those skilled in theart, that the reversed portion of the current will contain a componentof charge density modulation corresponding in frequency to the velocitymodulation produced by the tubular electrode 232. Consequently as suchreversed portion passes through the electrode it will induce currentvariations therein having a frequency corresponding to the frequency oftuning of the oscillator circuit. These induced currents will underproper conditions be such as to make the oscillations of the circuitself-sustainto maintain the operation system.

As illustrated the anode 235 is tilted at such an angle that thereversed current component intersects a boundary diaphragm 243, and isthus prevented from entering the modulating space which contains thegrid 23L For the sake of simplicity the structural features of theinvention have so far been described solely in connection with anend-to-end arrangement of the electrodes. Such an arrangement is by nomeans essential, however, and in Figs. and 21 there is shown an exampleof an entirely different structure which nevertheless embodies theprinciples of the invention.

Referring to Fig. 20, there is shown a discharge device in which theelectron source comprises a hairpin filament 250 which is of substantiallongitudinal extent. This filament or cathode is mounted in side by siderelationship with a grid l adapted partially to shield the same and isarranged diametrically opposite to an anode 252.

Within the grid 25! there is provided an addiof the oscillating tionalgrid 253 which is similarin function to the "boundary diaphragms"hereinbefore described. That is to say, the grid 253 defines amodulating space which may enclose a control electrode structure, hererepresented in the form of a gridlike spiral 254. As a matter ofpractical design the grid 253 and the control electrode 254 may bearranged as the respective elements of a concentric transmission linewhich is of such dimensions as to be properly tuned to the frequency ofa control potential to be applied thereto (see Fig.

In the operation of the device an electron stream is developed in thedirection of the anode 252 by means of a relatively high potential (say300 volts) impressed between the cathode 250 and the intermediate grid253. Excessive electron emission from the cathode is prevented bycharging the grid 25l to a relatively low potential, on the order of afew volts positive or negative, with respect to the cathode.

As the electron stream enters the modulating space formed by the grid253, it may be velocity modulated by means of a suitably varyingpotential impressed on the grid 254 by an input circuit 255, as shown inFig. 21 (or alternatively, by the practical arrangement indicated inFig. 22). The velocity modulation then may be converted into chargedensity modulation by maintaining the anode 252 at a sufilciently lowpotential to reverse at least a portion of the beam. In this case thereflected components of the beam will be largely collected by the grid25| and will thus be prevented from returning to the modulating space.

Energy may be abstracted from the charge density modulated components ofthe electron stream by means of the anode 252 in combination with asuitable output circuit typically represented at 258, and comprising acondenser 259 and an inductance 260.

It is an advantage of the construction just described that an electronstream of considerable cross-sectional area may be employed. For thisreason, in some cases the power which may be handled by the device willbe in excess of that possible with devices employing a pencil-likeelectron beam as in the other structures described.

' While I have described the invention primarily in connection with pureelectron discharges, the principles of the invention are equallyapplicable to the control and .conversion of currents 22,506 ing so thatno external energy need be supplied involving charged particles otherthan electrons. For example, if one has due regard to the dimensionalchanges required by the different velocities and masses involved, adirect application of the invention may be made to discharge devicesutilizing positive ion currents. I aim in the appended claims to coverall variations in structure and application which fall within the truespirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination, a discharge device including a thermionic cathode fordeveloping an electron beam of substantially constant average intensity,a pair of spaced diaphragms arranged transverse to the beam path, suchdiaphragms being provided with openings to permit passage of the beamtherethrough and being normally maintained at a fixed potential withrespect to the cathode, an electrode arranged within the space boundedby the diaphragms for controlling the potential level of an intermediateregion of such space, means including a source of control potentialeffective during the use of the device to raise and lower the potentialof the control electrode at such a rate that individual electronstraversing the space are similarly affected in velocity as they approachand recede from the said intermediate region, and means including autilization circuit for effectively abstracting energy at alternatingpotentials from the beam after its issuance from the modulating space.

2. In combination, a discharge device comprising means including athermionic cathode for developing an electron beam of substantiallycon.- stant average intensity and velocity, a pair of spaced diaphragmsarranged transversely to the beam, both of said diaphragms beingprovided with openings to permit passage of the beam therethrough andbeing normally maintained at a fixed potential with respect to oneanother, a control electrode structure within the space defined by saiddiaphragms for controlling the potential of a region thereof traversedby the beam, means including a portion of said control electrodestructure for maintaining an intermediate part of said region at a loweraverage potential than the end portions thereof, means including asource of control potential for raising and lowering the potential levelof the control electrode structure as a whole with respect to thepotential of said diaphragms, and means for abstracting energy from theelectron beam after its passage through said space.

3. In high frequency apparatus the combination which includes means fordeveloping an electron beam, a plurality of apertured conductingdiaphragms arranged transversely of the beam and defining a series ofmodulating spaces to be successively traversed by the beam, a controlelectrode in eachof the modulating spaces, means including a source ofcontrol potential for simultaneously raising and lowering the potentiallevel of the various control electrodes with respect to the adjacentconducting diaphragms, said control electrodes and spaces being soproportioned with reference to the average beam velocity and thefrequency of the control potential that any given electron in the beamis similarly affected in velocity as it passes through each of themodulating spaces, and means including an alternating current circuitfor effectively utilizing the cyclical variations existing in the beamafter its passage through the modulating spaces.

4. In combination, means for developing a veoases modulated portionthereof for converting kinetic energy in the latter portion intoelectrical energy to be utilized in an external circuit, and means forneutralizing the effects of potential variations of said electrode onthe velocity modulated beam.

5. In combination, means for developing- 9. velocity modulated electronbeam, means for reversing at least a portion of the beam in order toconvert its velocity modulation into charge density modulation, meansincluding an electrode in energy-exchanging relation with both thevelocity modulated beam and the reversed charge density modulatedportion thereof for converting kinetic energy in the latter portion intoelectrical energy to be utilized in an external circuit, anda secondelectrode in energy-exchanging relation with only the velocity modulatedportion of the beam, said second electrode being variable in potentialwith the first electrode and serving to neutralize the effects on thevelocity modulated beam of variations in potential of said electrode.

6. In an amplifier or detector for use under conditions such thattransit time phenomena play a controlling part in the operation of theapparatus, the combination which includes means for developing a streamof electrons, a pair of spaced .conducting members arranged to besuccessively traversed by the stream, an electrode located within thespace bounded by the members, said electrode comprising a hollowconducting tube substantially coaxial with the beam and extend-' ing towithin a short distance of each of the members, means including an inputcircuit for impressing a cycylically variable potential of predeterminedfrequency between the tube'and the members, the axial length of the tubebeing so correlated to the average velocity of the electron stream thatat the said predetermined frequency of operation any given electron inthe stream is similarly affected in velocity as it approaches andrecedes from the tube, and means including an output circuit foreffectively utilizing the cyclical variations occurring in the stream'subsequent to its issuance from the space bounded by the said conductingmembers.

7. In apparatus for use under conditions such that transit timephenomena play a controlling part in the operation of the apparatus, thecombination which comprises means including a cathode for developing astream of electrons, a

pair of spaced conducting members arranged to be successively traversedby the stream, means for maintaining said members at a fixed potentialwith respect to the cathode, an electrode of negligible axial extentarranged midway between said members, and means including a source ofcontrol potential for cyclically raising and lowering the potential ofsaid electrode with respect to the conducting members, the spacingbetween said electrode and each of the members being such that theelectron transit time from either member to the plane of the electrodecorresponds at least approximately to an odd number of half cycles ofthe control potential.

8. In high frequency apparatus, means including a cathode for developingan electron stream of to within a short distance of each of thememsubstantially constant average intensity and velocity,-meansincluding a control electrode acting symmetrically on the stream toproduce'longitudinai velocity modulation thereof. means shielding thesaid control electrode from the cathode to avoid the production ofappreciable charge density varhtions in the vicinity of the electrode,means providing a shielded drift space to be traversed by the velocitymodulated stream sub-' sequent to its issuance from the electrode, suchspace being of sufllcient length to permit the conversion of thevelocity modulation of the beam into charge density modulation ofsubstantially greater magnitude, and circuit means for effec- 'tivelyutilizing the variations existing in the charge density modulated streamsa e through the drift space.

9. In high frequency apparatus, means for producing a beam of simflarlycharged particles, a modulating electrode traversed by the beam,shielding means for defining a region of fixed potential level on eitherside of said electrode, means for cyclically raising and lowering thepotential of said electrode with respect to said shielding means at sucha rate that individual particles traversing the electrode are similarlyaffected in velocity as they approach and recede from such electrode,and means including a high frequency circuit for utilizing conductioncurrent variations occurring in the beam after its issuance after itspas from the second of the said regions of fixed potential level.

10. In high frequency apparatus, means including a cathode for producinga beam of electrons of substantially constant average intensity andvelocity, a pair of spaced conducting members arranged to besuccessively traversed by the beam, means for maintaining said membersat fixed potential with respect to the cathode, a

modulating electrode within the space between said members. means forcyclically raising and lowering the potential of said electrode withrespect to said members at such a rate that any given electrontraversing the said space is similarly affected in velocity as itapproaches and recedes from said electrode, and means including a highfrequency circuit for utilizing conduction current variations occurringin the beam after its issuance from the space bounded by the saidconducting members. 7

11. In high frequencyapparatus, means for producing a beam'of similarlycharged particles, a pair of spaced conducting members arranged to besuccessively traversed by the beam, a modulating electrode structurewithin the space between said members and defining an equipotenthattransit time phenomena play a controlling part in the operation of theapparatus, the combination whichincl'udes means for developing a streamof electrons, a pair of spaced conducting members arranged to besuccessively traversed by the stream, a hollow conducting tube withinthe space between said members, said tube being substantially coaxialwith the beam and extending bers, circuit means for impressing acyclically variable potential of predetermined frequency between thetube and the members, the axial length of the tube being so correlatedto the average velocity of the electron stream that at the saidpredetermined frequency of operation any given electron in the stream issimilarly affected in velocity as it approaches and recedes from thetube. and circuit means for effectively utilizing the cyclicalvariations occurring in the stream subsequent to its issuance from thespace bounded by the said conducting members.

13. In high frequency apparatus, means for developing a beam ofsimilarly charged particles, means for modulating the beam at aparticular frequency to produce cyclically recurrent variations axiallyof the beam, a utilization circuit of such character as to be readilyexcited at the said particular frequency, and an output electrode systemcoupled to the said utilization circuit and arranged to be traversed bythe beam after its traversal of the said modulating means, the saidoutput system comprising an output electrode traversed by the beam andshielding means defining a region of fixed potential level on eitherside of the said electrode, the axial dimensions of the said outputsystem being so correlated to the average beam velocity that as a resultof potential variations of the said electrode attributable to itscoupling with the utilization circuit, any given particle in the beam issimilarly affected in velocity as it approaches and recedes from theelectrode.

14. In high frequenc apparatus, means for developing a beam of electriccharges, means for modulating the beam at a particular frequency toproduce cyclically recurrent variations axially of the beam, and anoutput system arranged to be traversed by the beam subsequent to theoperation of the said last-named means thereon, said output systemincluding a utilization circuit of such character as to be readilyexcited at the said particular frequency, a pair of spaced conductingmembers which are successively traversed by the beam, and an electrodestructure arranged within the space bounded by said members and definingan equipotential region therein, the said electrode structure beingconnected to the said utilization circuit and the said equipotentialregion being of such axial extent that, as a result of potentialvariations of the structure produced by said circuit, any given elementof the beam is similarly affected in velocity as it approaches andrecedes from such region.

15. In high frequency apparatus, means for developing a beam of electriccharges, means acting on the beam at a particular frequency to producerecurrent charge density variations axially thereof, and an outputsystem arranged to be traversed by the beam subsequent to the operationof the said last-named means thereon, said output system including acircuit of such character as to be readily excited at the saidparticular frequency, a pair of spaced conducting members arranged to besuccessively traversed by the beam, and a hollow tubular electrodestructure positioned coaxially with the beam between said members andslightly spaced from the members at its extremities so as to provide apair of spaced gaps, said electrode structure being connected to thesaid utilization circuit and being of such axial extent that any givenelement of the beam is similarly affected in velocity by the potentialgradients produced in both gaps by the action of said circuit.

16. In apparatus for use under conditions such that transit timephenomena play a controlling preciably greater magnitude,

part in the operation of the apparatus, the combination which comprisesmeans for developing an electron beam of substantially constant averageintensity and velocity, an input electrode system comprising a pair ofspaced conducting members arranged to be successively traversed by thebeam and a hollow conducting tube within the space between said members,said tube beingsubstantially coaxial with the beam and extending towithin a short distance of each of the members, means for impressing acyclically variable potential of predetermined frequency between thetube and the members, the axial length of the tube being so correlatedto the average velocity of the electron stream as to assure effectivemutual reaction therewith at the said predetermined frequency ofoperation, an output electrode system structually similar to the saidinput system and arranged to be traversed by the beam after itstraversal of the input system, and circuit means coupled to the saidoutput electrode system and adapted to be excited by the reaction of thebeam on such system.

17. In an amplifier or detector for use under conditions such thatoperation is controlled by transit time phenomena, the combination whichcomprises means including a cathode for developing an electron stream ofsubstantially constant average intensity and velocity, a controlelectrode structure acting symmetrically on the stream and operable toproduce longitudinal velocity modulation thereof, means for suflicientlyshielding the operative portion of said control electrode structure fromthe cathode to avoid the production of substantial varriations in thecathode emission as a result of the action of such structure, meansconnected with said control electrode structure for exciting the same atultra-high frequency, means providing a shielded drift space to betraversed by the velocity modulated beam after its traversal of the saidcontrol electrode structure, such space being of sufficient length topermit the conversion of the velocity modulation of the beam into chargedensity modulation of apand means includeifectively utilizing the beamafter its passage ing an output circuit for variations existing in thethrough the drift space.

18. In apparatus for use under conditions such that transit timephenomena play a controlling part in the operation of the apparatus, thecombination which comprises means for developing an electron beam, amodulating electrode system comprising a pair of spaced conductingmembers arranged to be successively traversed by the beam and a hollowconducting tube within the space between said members, said tube beingsubstantially coaxial with the beam and extending to within a shortdistance of each of the members, means for impressing a cyclicallyvariable potential of predetermined frequency between the tube and themembers, the axial length of the tube being so correlated to the averagevelocity of the electron stream that at the said predetermined frequencyof operation any given electron in the beam is similarly afiected invelocity as it approaches and recedes from the tube, means providing adrift space to be traversed by the beam and wherein velocity variationsproduced by said modulating system may be converted into charge densityvariations, an energy-abstracting electrode system structurally similarto the said modulating system and arranged to be traversed by the beamafter its issuance from the drift space, and circuit means coupled tothe last named electrode system of such character as to be readilyexcited by the reaction of the beam on such system.

19. A method of amplifying high frequency impulses which comprisesproducing a beam of electrons of uniform velocity, producinglongitudinal velocity modulation of the beam in accordance with theimpulses to be amplified, directing the modulated beam along a shieldedpath which is long in comparison with the distance traversed by the beamduring one cycle of the impulses to be amplified, thereby setting up inthe beam longitudinal variations in charge density correspondmg to thepreviously produced velocity modulation thereof, and utilizing saidcharge density variations to produce an output current.

20. In an amplifier or detector for use under conditions such thatoperation is controlled by transit time phenomena, the combination whichcomprises means for producing a beam of electrons of substantiallyuniform velocity, means for producing longitudinal velocity modulationof the beam, means providing a shielded space to be traversed by thevelocity modulated beam, such space being of sufficient length to permitthe conversion of the velocity modulation of the beam into chargedensity modulation of appreciably greater magnitude, and means includingan output circuit for effectively utilizing the variations existing inthe beam after its passage through the said space.

21. In an amplifier or detector for use at ultrahigh frequencies, thecombination which includes means for producing a beam of electrons ofsubstantially uniform velocity, electrode structure defining a narrowgap to be traversed by the beam, means acting on the beam at the saidgap to produce longitudinal velocity modulation thereof in accordancewith the signals to be amplified or detected, means providing a shieldedspace to be traversed by the velocity modulated beam after having passedthe said gap, such space being of sufiicient length to permit theconversion of the velocity modulation of the beam into charge densitymodulation of appreciably greater magnitude, and means for utilizing thevariations existing in the beam after its passage through the said spaceto produce an output current.

WILLIAM C. HAHN.

